Once weekly administration of the dopamine agonist, cabergoline, will lower serum prolactin concentrations in a dose dependent manner and will promote reduction in tumor size in patients with a prolactin secreting pituitary macroadenoma. Cabergoline, a long-acting dopamine agonist, was used to treat men and women with a prolactin secreting macroadenoma. This drug was effective in lowering serum prolactin and in reducing pituitary tumor size. The results were published, Biller et al, 1996 in the Journal of Clinical Endocrinology. Cabergoline was approved by the FDA for treatment of hyperprolactinemia in December, 1996. This study has been completed.